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Exchange Server 2013 is vital for many businesses, so administrators are always in search of new ways to improve performance, enhance security and boost availability. One area that deserves some consideration is virtualization. Exchange 2013 supports major hypervisors such as Hyper-V with Windows Server 2012 R2, ESXi and XenServer. But administrators and architects must understand the limitations and caveats that remain when virtualizing Exchange 2013.
Exchange roles can be sensitive to computing resources, so the goal is to allocate enough computing resources to avoid shortages. However, this approach to provisioning is slowly changing as hypervisor and Exchange technologies evolve. Early VM provisioning practices often used static resource allocation and ample reservation sizes. But the latest guidance from VMware suggests that Exchange 2013 can tolerate flexible provisioning with tools such as VMware's distributed resource scheduler (DRS); use reservations and avoid DRS only when service level agreements demand minimum computing resources. Generally, a VM with a single vCPU with a 1-to-1 virtual-to-physical CPU ratio is preferred for Exchange VMs; use multiple vCPUs only if the Exchange VM can really use multiple vCPUs. Processors that support second-level address translation can also boost VM performance.
Memory provisioning is less forgiving on Exchange VMs. As a rule, take the time to determine the optimum memory size for an Exchange VM and don't over-commit memory to VMs running Exchange roles. Use reservations to prevent memory over-commitment. If the hypervisor uses memory ballooning (such as ESXi), don't disable or remove the balloon driver because unused memory from one VM can shift to another VM that requires more memory. Tools like DRS can automatically migrate non-critical VMs to other servers and to free resources for critical VMs (like Exchange roles), so DRS and vMotion can be useful in modern Exchange optimization.
When possible, deploy VM files on shared storage to use migration, high availability and workload balancing tools (such as vMotion, HA and DRS for VMware environments). Establishing multiple paths between servers and storage is critical for resilient storage access. When selecting a virtual SCSI adapter, the default LSI Logic SAS adapter is usually adequate, but high-end Exchange deployments with thousands of end users per mailbox server might benefit from specialized virtual SCSI adapters such as VMware's Paravirtual SCSI (PVSCSI) adapter. It might even be possible to access Exchange data on network-attached storage, but it's not officially supported.
This is part five in a series on improving your Exchange 2013 setup.
Part three: Strengthen Exchange security
Part four: Load balance Exchange workloads
Dig Deeper on Microsoft Exchange Server Administration Tools